Dielectric fluid compositions for enhanced thermal management

ABSTRACT

A dielectric fluid composition for electrical apparatus comprises a functionalized 12-hydroxy stearic acid having desirable properties including a pour point less than −30° C. and a fire point greater than 250° C. It may be prepared by a process wherein 12-hydroxy methyl stearate is transesterified by reaction with a C3-C20 alcohol to form an alkyl-12-hydroxy stearate, followed by esterification thereof with a linear or branched C4-C20 carboxylic acid. This acid may be a free acid chloride, a fatty acid, a carboxylic acid anhydride, or combination thereof. The resulting functionalized 12-hydroxy stearic acid exhibits improved thermoxidative capability, low temperature flowability, and increased fire point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority fromthe U.S. Provisional Patent Application No. 61/541,584, filed on Sep.30, 2011, entitled “DIELECTRIC FLUID COMPOSITIONS FOR ENHANCED THERMALMANAGEMENT,” the teachings of which are incorporated by referenceherein, as if reproduced in full hereinbelow.

BACKGROUND

1. Field of the Invention

The invention relates particularly to the field of dielectric fluidsused for thermal management of transformers. More particularly, itrelates to improved compositions that provide both electrical insulationand/or heat dissipation for transformers and other apparatus.

2. Background of the Invention

Thermal management of transformers is known to be critical for thesafety of transformer operation. Although conventional transformersoperate efficiently at relatively high temperatures, excessive heat isdetrimental to transformer life. This is because transformers containelectrical insulation which is utilized to prevent energized componentsor conductors from contacting, or arcing over, the other components,conductors, or internal circuitry. In general, the higher thetemperatures experienced by the insulation, the shorter its life. Wheninsulation fails, an internal fault or short circuit, sometimes leadingto fire, may occur.

In order to prevent excessive temperature rise and premature transformerfailure, transformers are generally filled with a liquid coolant todissipate the relatively large quantities of heat generated duringnormal transformer operation. The coolant also functions to electricallyinsulate the transformer components as a dielectric medium. Thedielectric liquid must be able to cool and insulate for the service lifeof the transfer, which is in a number of applications in excess oftwenty years. Because dielectric fluids cool the transformer byconvection, the viscosity of a dielectric fluid at various temperaturesis one of the key factors in determining its efficiency.

Mineral oils have been tried in various dielectric formulations,particularly because they may offer a degree of thermal and oxidativestability. Unfortunately, however, mineral oils are believed to beenvironmentally unfriendly and may exhibit unacceptably low fire points,in some cases as low as 150 degrees Celsius (° C.) which is undesirablyclose to the maximum temperatures to which a dielectric fluid is likelyto be exposed during use in a given application, such as a transformer.Because of their low fire points, researchers have sought alternativedielectric materials.

In this search for alternatives, vegetable oils were early-identified asa dielectric medium that could be environmentally friendly and exhibitthe desired characteristics of desirably high fire points (significantlygreater than 150° C.) and desirable dielectric properties. They may alsobe biodegradable within a short time. Finally, they may offer enhancedcompatibility with solid insulating materials.

Unfortunately, vegetable oil based fluids may suffer from their owndrawbacks when compared with mineral oils. For example, vegetable oilsmay tend to have higher pour points, e.g., greater than 0° C. This isproblematic for the many applications where a pour point at or below−15° C. may be required. They may also have an undesirably higherviscosity than a mineral oil based fluid. Thus, researchers seek toidentify dielectric fluids that can operate safely and properly within abroad temperature range of from about −15° C. to about 110° C., andwhich are thermally and oxidatively stable therein.

Researchers looking for alternative have identified a number of possiblefluids. For example, U.S. Pat. No. 6,340,658 B1 (Cannon et al.)describes a vegetable oil-based electrically-insulating fluid, which isenvironmentally friendly and has a high flash point and high fire point.The base oil is hydrogenated to produce maximum possible stability ofthe oil. Vegetable oils are selected from, e.g., soybean oil and cornoil.

U.S. Patent Publication 2008/0283803 A1 describes a dielectriccomposition comprising at least one refined, bleached, winterized,deodorized vegetable oil and at least one antioxidant. The dielectricfluid further comprises at least one synthetic ester, wherein thesynthetic ester is a bio-based material. The patent defines the term“synthetic ester” as referring to esters produced by a reaction between(1) a bio-based or petroleum derived polyol: and (2) a linear orbranched organic acid that may be bio-based or petroleum derived. Theterm “polyol” refers to alcohols with two or more hydroxyl groups.Suitable examples of the bio-based synthetic esters included are thoseproduced by reacting a polyol with an organic acid with carbon chainlengths of C8-C10 derived from a vegetable oil such as, for example,coconut oil. The synthetic esters also included syntheticpentaerythritol esters with C7-C9 groups. Other polyols suitable forreacting with organic acid to make the synthetic esters includeneopentyl glycol, dipentaerythritol, and e-ethylhexyl, n-octyl,isooctyl, isononyl, isodecyl and tridecyl alcohols.

Despite these and other efforts by a variety of researchers, there isstill a need to develop dielectric fluids that have the desiredcombination of properties as well as economic viability and capabilityfor biodegradation.

SUMMARY OF THE INVENTION

In one aspect the invention is a dielectric fluid composition forelectrical apparatus comprising a functionalized 12-hydroxy stearic acidhaving at least one property selected from a number average molecularweight (M_(n)) from 400 Daltons (Da) to 10,000 Da; a dielectricbreakdown strength greater than 20 kilovolts/1 mm gap (kV/mm); adissipation factor less than 0.2 percent (%) at 25° C.; a fire pointgreater than 250° C.; a kinematic viscosity less than 35 centistokes(cSt) at 40° C.; a pour point less than −30° C.; an acidity less than0.03 milligrams potassium hydroxide per gram sample (mg KOH/g); and acombination thereof.

In another aspect the invention is a process for preparing a dielectricfluid composition comprising (a) reacting 12-hydroxy methyl stearate anda linear or branched C3 to C20 alcohol under conditions suitable to forman alkyl-12-hydroxy stearate; and (b) reacting the alkyl-12-hydroxystearate and a carboxylic acid selected from the group consisting oflinear and branched C4-C20 free acid chlorides, fatty acids, carboxylicacid anhydrides, and combinations thereof, under conditions suitable toform a functionalized 12-hydroxy stearic acid.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides a dielectric fluid composition that is useful forthermal management in electrical apparatuses, and has a variety ofdesirable properties. These properties may include, in specific andnon-limiting embodiments, a property, or combination of properties,selected from a dielectric breakdown strength greater than 20 kV/mm gap,a dissipation factor less than 0.2% at 25° C., a fire point greater than250° C., a kinematic viscosity less than 35 cSt at 40° C., a pour pointless than −30° C., and an acidity less than 0.03 mg KOH/g. In additionit may exhibit a number average molecular weight (M_(n)) ranging from400 Da to 10,000 Da, which helps to ensure a viscosity that is useful inthe target applications. The American Society for Testing and Materials(ASTM) standards used to determine these properties are indicated inTable 1 hereinbelow.

TABLE 1 Property and units ASTM standard Dielectric breakdown strength,kV/mm gap ASTM D1816 Dissipation factor, % at 25° C. ASTM D924 Firepoint, ° C. ASTM D92 Kinematic viscosity, cSt at 40° C. ASTM D445 Pourpoint, ° C. ASTM D97 Acidity, mg KOH/g ASTM D974

The dielectric fluid compositions may be prepared starting with either acommercially available product, 12-hydroxy methyl stearate (12-HMS), or,in a pre-process step, from a commonly known and widely availablevegetable oil, castor oil. Castor oil comprises primarily ricinoleicacid as its major component (approximately 90 percent of the fatty acidchains), and, in lesser amounts (approximately 10 percent of the fattyacid chains), oleic and linoleic acids, all of which are based on18-carbon chains. Castor oil itself suffers from relatively poorthermoxidative stability and low temperature flowability.

In order to begin with castor oil as a precursor, the castor oil maytypically be hydrogenated and then transesterified by reaction, with,e.g., methanol, to form 12-HMS. This 12-HMS may then be separated fromthe remaining castor oil products. Since ricinoleic acid includesunsaturation at the ninth (9^(th)) carbon of the 18-carbon chain,hydrogenation serves to eliminate this unsaturation. Hydrogenation ofcastor oil is known in the art and this hydrogenation step mayoptionally be included simply as a pre-process step with the presentinvention.

Once the 12-HMS has been procured or prepared, it is ready for use inthe first step of the inventive process. This step involves atransesterification of the 12-HMS wherein it is reacted with a linear orbranched C3 to C20 alcohol under suitable conditions to form thealkyl-12-hydroxy stearate. In preferred embodiments this alcohol may bea linear or branched C6 to C12 alcohol, and more preferably a linear orbranched C8 to C10 alcohol. Preferred conditions for this reactioninclude a stoichiometric excess of the alcohol, more preferably fromthree (3) to six (6) times the amount that would be stoichiometric withthe 12-HMS, and most preferably four (4) to six (6) times. Also includedis use of an effective transesterification catalyst selected from, forexample, sodium and potassium bases such as sodium methoxide (NaOCH₃);alkyl tin oxides, such as tri-n-butyl tin oxide and dibutyl tindilaurate; titanate esters; acids such as hydrochloric and sulfuric; andcombinations thereof; a temperature ranging from 100° C. to 200° C.,more preferably from 120° C. to 190° C., and most preferably from 140 °C. to 180° C.; at atmospheric pressure and followed by any suitabledistillation such as wiped film evaporation. In this first step reactionthe alkyl moiety of the alkyl-12-hydroxy stearate comes from the alcoholresidue, i.e., the R in the alcohol formula ROH. Non-limiting examplesof C3-C20 alkyl groups would include, in particular embodiments, linearmoieties including hexyl, octyl, decyl, and dodecyl, and theircorresponding branched moieties, such as ethylhexyl and ethyloctyl.

Once the alkyl-12-hydroxy stearate has been prepared—for example, via areaction of 12-HMS and 2-ethyl hexanol resulting in atransesterification product that is 2-ethylhexyl-12-hydroxy stearate, orvia a reaction of 12-HMS and octanol resulting in a transesterificationproduct that is octyl-12-hydroxy stearate—it is then further esterified,in a second process step, by reacting it with an esterification, orcapping, agent. This agent is a linear or branched C4-C20, preferably aC6-C12, and more preferably a C8-C10, carboxylic acid. Such carboxylicacid may be selected from free acid chlorides, fatty acid chlorides,carboxylic acid anhydrides, and combinations thereof. The purpose ofthis second step is to functionalize the alkyl-12-hydroxy stearate,i.e., to end-cap the free hydroxyl groups, thereby increasing branchingto raise the fire point while limiting the viscosity build up.

When this second step is carried out under suitable conditions, theresult is a capped oxyalkanoic ester product derived from the12-hydroxy-alkyl-stearate, i.e., it is a functionalized 12-hydroxystearic acid. For example, if the first step transesterification productis 2-ethylhexyl-12-hydroxy stearate, and the second step esterification(i.e., capping) is done using a carboxylic acid chloride such asdecanoyl chloride, the resulting product is 2-ethylhexyl-12-oxydecanoylstearate. If the first step transesterification product is2-ethylhexyl-12-hydroxy stearate, and the second step esterification isdone using octanoyl chloride, the result is 2-ethylhexyl-12-oxyoctanoylstearate. If the first step product is 2-ethylhexyl-12-hydroxy stearate,and the second step esterification is done using isobutyric anhydride,the result is 2-ethylhexyl-12-oxyisobutanoyl stearate. Those skilled inthe art will understand that there are many other embodiments of theinvention, depending upon the alcohol and capping (esterification) agentselected, and that these examples are provided for illustrative purposesonly.

Preferred conditions for this second step reaction include a slightstoichiometric excess of the capping agent (preferably from 1 molarpercent (mol %) to 10 mol %, more preferably from 0.5 mol % to 5 mol %,and most preferably from 0.1 mol % to 0.2 mol %). Also included is theuse of an effective transesterification catalyst selected from, forexample, sodium and potassium bases such as sodium methoxide (NaOCH₃);alkyl tin oxides, such as tri-n-butyl tin oxide and dibutyl tindilaurate; titanate esters; acids such as hydrochloric and sulfuric; andcombinations thereof; a temperature ranging from 100° C. to 200° C.,more preferably from 120° C. to 190° C., and most preferably from 140°C. to 180° C.; at atmospheric pressure followed by any suitabledistillation such as wiped film evaporation. It is noted that atcommercial scale, a free carboxylic acid, decanoic acid, may be moremore economical than a fatty acid chloride or an anhydride.

The following process schematic is provided as FIG. 1 in order toillustrate the process aspect of the invention. For illustrativepurposes only, FIG. 1 shows use of 2-ethyl hexanol as thetransesterifying alcohol; NaOCH₃ as the catalyst for thetransesterification; and a transesterification temperature of 160° C. Inthe second step of FIG. 1, the esterification of the2-ethylhexyl-12-hydroxy stearate is accomplished by reaction withdecanoyl chloride to form the capped final dielectric fluid, which is2-ethylhexyl-12-oxydecanoyl stearate.

When prepared as described herein, the novel compositions which may beprepared by the process described hereinabove may exhibit highlydesirable properties. For example, they may have an M_(n) from 400 Da to10,000 Da, preferably 500 Da to 5,000 Da; a dielectric breakdown greaterthan 20 kV/mm gap, preferably greater than 25 kV/mm gap; a dissipationfactor less than 0.2% at 25° C., preferably less than 0.1% at 25° C.; afire point greater than 250° C., preferably greater than 300° C.; akinematic viscosity less than 35 cSt at 40° C., preferably less than 30cSt at 40° C.; a pour point lower than −30° C., preferably lower than−40 ° C.; and/or an acidity less than 0.03 mg KOH/g, preferably lessthan 0.025 mg KOH/g. In some embodiments two or more of these propertiesmay be characteristic of the compositions.

A further advantage to the dielectric fluid compositions of the presentinvention is that they may be used neat, i.e., at 100 weight percent (wt%) of a dielectric fluid being used in an application such as in atransformer, or they may be combined with, and compatible with, avariety of other dielectric fluids for such applications, at levelsranging from 1 wt % to 100 wt %. In particular embodiments it may bepreferred that the inventive compositions comprise from 30 wt % to 90 wt% of such combination fluids, and in more preferred embodiments such maycomprise from 40 wt % to 90 wt %, and most preferably from 50 wt % to 90wt %.

Additional dielectric fluids that may be combined with the dielectricfluid compositions of the present invention may include, in non-limitingexample, natural triglycerides such as sunflower oil, canola oil, soyoil, palm oil, rapeseed oil, cottonseed oil, corn oil, coconut oil, andalgal oils; genetically modified natural oils such as high oleicsunflower oil and high oleic canola oil; synthetic esters such aspentaerythritol esters; mineral oils such as UniVolt™ electricalinsulating oils (available from ExxonMobil); poly alpha olefins such aspolyethylene-octene, -hexane, -butylene, -propylene and/or -decalenebranched, random co-polyoligomers having M_(n) values ranging from 500to 1200 Da; and combinations thereof. It will be obvious to thoseskilled in the art that inclusion of additional dielectric and/ornon-dielectric fluids may significantly alter properties, and thattherefore the effect of such should be taken into account according tothe targeted application.

Among the advantages of the dielectric fluid compositions of theinvention is that they are biodegradable, obtained from renewableresources, and are generally classified as environmentally friendly.Furthermore, because of their relatively high fire points, they aregenerally less flammable than many of their dielectric competitors. Theyalso show good thermal and hydrolytic stability properties that mayserve to extend the insulation system's life.

EXAMPLES Example 1 (12-HMS/2-Ethyl-1-hexanol/Octanoyl Chloride)

Day 1: 164.75 grams (g) of 2-ethyl-1-hexanol is weighed into a 1000milliliter (mL) three neck round bottom flask. A condenser, Dean StarkTrap, thermometer with a thermowatch temperature regulator, an overheadmechanical stirrer, stopper, and N₂ inlet are added. The stirrer isturned on. A half-cube of sodium (Na) metal (˜0.102 g, flattened, cutinto small pieces) is added to the flask. The heat is turned up to 60°C. The Na dissolves after 45 minutes. 100.23 g of 12-HMS is added to theflask. Insulation is wrapped around the flask. The heat is turned up to160° C. Methanol overhead is collected. The reaction mixes for 6 h andis allowed to continue overnight.

Day 2: After 7 h, GC confirms the reaction is complete and the heat isturned off. 100 mL of toluene is added once the reaction mixture returnsto room temperature. The sample is put into a separatory funnel andthree (3) 50 mL (each) washes with 1N HCl are done to neutralize the Na.The aqueous layer is discarded. The organic layer is cloudy and put intoa 500 mL Erlenmeyer flask. Magnesium sulfate (MgSO₄), anhydrous powder,is added to the Erlenmeyer flask until the MgSO₄ stops clumping in theflask. The solution is then clear. The MgSO₄ is filtered out using aBuchner funnel with a perforated plate attached to an Erlenmeyer. Toremove the toluene and excess 2-ethy-1-hexanol, the sample is evaporatedusing a rotary evaporator (“rotavap”) secured with a pump. The waterbath is first set at 40° C. to remove the Toluene, and then bumped up to90° C. to remove the 2-ethyl-1-hexanol. GC confirms there is still anexcess of 2-ethyl-1-hexanol, so the sample is put through the WFE usingthe following conditions.

TABLE 2 Collection conditions for 2-ethylhexyl-12-hydroxy stearate.Jacket Cold Finger Stir Speed Pressure Flow Rate (° C.) (° C.) (rpm)(mtorr) (mL/min) 150 10 484 100 2.0 100 mtorr = about 0.01 kilopascals(kPa)

Day 3: Addition of octanoyl chloride (1.1 mole excess) is carried out byfirst weighing 107.00 g of product into a 500 mL three neck round bottomflask. A condenser, thermometer with a thermowatch temperatureregulator, an overhead mechanical stirrer, stopper, and N₂ inlet areadded. The stirrer is turned on. 100 mL of toluene is added. Using anaddition funnel, 44.87 g of octanoyl chloride is added. After 1 h, GCconfirms that the reaction is complete.

100 mL of methanol is added to the sample. The sample is put on therotavap to remove the toluene and methanol. GC confirms that somesolvent is still present in the sample. The sample is then run down theWFE using the same conditions stated earlier. The overheads arediscarded.

The sample is put into a freezer overnight, and in the morning it isdiscovered that it has not frozen. Acid number is 0.45 mg KOH/g.

Example 1 12-HMS/ME-810* (*a Roughly 50:50 wt % Blend of Octanoic andDecanoic Methyl Esters)

Day 1: 301.41 g of 12-HMS is weighed out into a 1000 mL three-neck,round-bottom flask. A condenser, Dean Stark Trap, thermometer with athermowatch temperature regulator, an overhead mechanical stirrer and N₂inlet are added. The stirrer is turned on. 410.90 g of ME-810 acid isadded. The reaction is heated to 170° C. and the progress of thereaction monitored by GPC until completion. The reaction is passedthrough the WFE using continuous flow and under following conditions.The bottoms (product) are collected and the overhead is discarded.

TABLE 3 Collection conditions for 12-HMS/ME-810. Jacket Cold Finger StirSpeed Pressure Flow Rate (° C.) (° C.) (rpm) (mtorr) (mL/min) 130 20 531200 6.0 200 mtorr = about 0.03 kPaThe product is primarily solids with some liquid and is deemedunacceptable for transformer fluid applications.

Example 3 12-HMS/2-Ethylhexanoic Acid

Day 1: 101.6 g of 12-HMS is weighed into a 500 mL three-neck,round-bottom, flask. A condenser, Dean Stark Trap, thermometer with athermowatch temperature regulator, an overhead mechanical stirrer,stopper, and N₂ inlet are added. 132.9 g of 2-ethylhexanoic acid isadded and the stirred reaction is heated to 170° C. After 3 h, the heatis turned off. Progress of the reaction is monitored by GPC. Uponcompletion, the product is put through the WFE using the followingconditions. The overhead is discarded. The solution is a clear, goldenyellow color.

TABLE 4 Collection conditions for 2-ethylhexanoic acid. Jacket ColdFinger Stir Speed Pressure Flow Rate (° C.) (° C.) (rpm) (mtorr)(mL/min) 130 20 397 200 4.3 200 mtorr = about 0.03 kPa

Example 4 12-HMS/2-Ethyl-1-hexanol/Decanoyl Chloride

Day 1: 400.66 g of 2-Ethyl-1-hexanol is weighed into a 2000 mL,three-neck, round bottom flask. A condenser, Dean Stark Trap to collectbi-product, thermometer with a thermowatch temperature regulator, anoverhead mechanical stirrer, and N₂ inlet are added. Na metal (0.411 g,flattened, cut into small pieces) is added to the stirred reaction andthe reaction heated to 60° C. The sodium dissolves after 1 h. 300.54 gof 12-HMS is added to the flask and heated to 160° C. The reaction ismixed overnight. The reaction continues through Day 2 and Day 3.

Day 4: GC confirms the reaction is complete and the reaction isneutralized with 2 mL of 12N HCl at room temperature. The sample isfiltered using a 2000 mL Erlenmeyer with a side arm and a 150-g Buchnerfunnel with filter paper. The sample is a very bright orange color. Toremove the excess 2-ethyl-1-hexanol, the sample is evaporated in vacuo.GC confirms there is still an excess of 2-ethyl-1-hexanol, so the sampleis put through the WFE using the following conditions.

TABLE 4 Collection conditions for excess 2-ethyl-1-hexanol. Cold FingerStir Speed Pressure Jacket (° C.) (° C.) (rpm) (mtorr) Flow Rate(mL/min) 140 10 492 100 1.5 100 mtorr = about 0.01 kPa

GPC analysis reveals the presence of dimeric species and the product isremoved via a WFE under the following conditions.

TABLE 5 Collection conditions for 2-ethylhexyl-12-hydroxyl stearate.Jacket Cold Finger Stir Speed Pressure Flow Rate (° C.) (° C.) (rpm)(mtorr) (mL/min) 240 20 387 100 1.5 100 mtorr = 0.01 kPa

GC analysis reveals that only the desired material is isolated in thedistillate or overhead fraction 350.12 g of this product is weighed intoa 2000 mL, three-neck, round-bottom flask. A condenser, thermometer witha thermowatch temperature regulator, an overhead mechanical stirrer andN₂ inlet are added. To the stirred reaction is added 177.32 g ofdecanoyl chloride (a 1.1 molar excess) dropwise at such a rate as tomaintain the temperature of the reaction at or below 50° C. The reactionis allowed to continue stirring with no heat overnight. GC analysisconfirms that the reaction is complete.

35 g of methanol is added to quench excess acid chloride and the sampleis put on the rotavap to remove the methanol. The sample is a clear,dark orange color. It is decided to put the sample through the WFE toremove any residual acid. The WFE is set using the same conditions asthe first WFE distillation. The overheads are discarded.

TABLE 6 Collection conditions for removal of methyl decanoate. ColdFinger Stir Speed Pressure Flow Rate Jacket (° C.) (° C.) (rpm) (mtorr)(mL/min) 140 10 492 100 1.5 100 mtorr = about 0.01 kPa378.12g of the sample is put into a 1000 mL, three-neck, round bottomflask. A thermometer with a thermowatch temperature regulator and anoverhead mechanical stirrer are added. 42 g of magnesium silicate isadded to the stirred reaction, then the reaction is heated to 70° C. for1 h. The sample is then cooled and filtered using a 90 millimeter (mm)microfiltration apparatus with filter paper with a 1 micrometer (um)pore size. Acid number of the final product is found to be 0.05 mg KOH/1g.

Example 5 12-HMS/2-Ethyl-1-hexanol/2-Ethylhexanoyl Chloride)

Day 1: 514 g of 2-ethyl-1-hexanol is weighed into a 2000 mL, three neckround bottom flask. A condenser, Dean Stark Trap, thermometer with athermowatch temperature regulator, an overhead mechanical stirrer,stopper, and N₂ inlet are added. The stirrer is turned on. An amount of1 cube of Na metal (flattened, cut into small pieces) is added to theflask. The heat is turned up to 60° C. The Na dissolves after 45minutes. 300 g of 12-HMS is added to the flask. Insulation is wrappedaround the flask. The heat is turned up to 160° C. The reaction mixesfor 6 h and is allowed to continue overnight. This continues through Day2 and Day 3.

On Day 4, after 4 h, GC confirms that the reaction is complete. 12 mL ofMethanol is collected. When the reaction is cooled, 100 mL of deionized(DI) water (H₂O) is added and neutralized with 150 mL 1N HCl. Threewater washes are done and separated using a separatory funnel. Theaqueous layer is discarded. The organic layer is put into a 2000 mLErlenmeyer flask. MgSO₄, anhydrous powder, is added to the Erlenmeyerflask until the MgSO₄ stops clumping in the flask. The solution is stillvery cloudy. A column prepared with Celite is set up, toluene is addedto the solution, and the solution is poured through the Celite column.The solution is then clear. To remove the toluene and excess2-ethyl-1-hexanol, the sample is evaporated using a rotavap undervacuum. The water bath is first set at 40° C. to remove the toluene, andthen the temperature is raised to 90° C. to remove the2-ethyl-1-hexanol. 326.81 g is recovered. GC confirms that an excess of2-ethyl-1-hexanol remains, so the sample is put through the WFE usingthe following conditions.

TABLE 7 Removal of excess 2-ethyl-1-hexanol. Jacket Cold Finger StirSpeed Pressure Flow Rate (° C.) (° C.) (rpm) (mtorr) (mL/min) 150 10 484100 2.0

Addition of 2-ethylhexanoyl chloride (1.2 mole excess) is carried outbatchwise as described hereinafter.

Batch 1: 80.77 g of product is weighed into a 500 mL three neck roundbottom flask. A condenser, thermometer with a thermowatch temperatureregulator, an overhead mechanical stirrer, stopper, and N₂ inlet areadded. The stirrer is turned on. 130 mL of toluene is added. Using anaddition funnel, 36.72 g of 2-ethylhexanoyl chloride is added. After 1h, the 2-ethylhexanoyl chloride is added and the heat is increased to120° C. After 1 h, GC confirms that the reaction is complete. Thereaction is stopped and put aside.

Batch 2: 80.04 g of product is weighed into a 500 mL, three-neck,round-bottom flask. A condenser, thermometer with a thermowatchtemperature regulator, an overhead mechanical stirrer and N₂ inlet areadded. The stirrer is turned on. 130 mL of toluene is added. Using anaddition funnel, 39.9 g of 2-ethylhexanoyl chloride is added. After 1 h,the 2-ethylhexanoyl chloride is added and the heat is increased to 120°C. After 1 h, GC confirms that the reaction is complete. The reaction isstopped and put aside.

Batch 3: 132.12 g of product is weighed into a 500 mL, three-neck,round-bottom flask. A condenser, thermometer with a thermowatchtemperature regulator, an overhead mechanical stirrer and N₂ inlet areadded. The stirrer is turned on. 150 mL of toluene is added. Using anaddition funnel, 69.93 g of 2-ethylhexanoyl chloride is added. After 1h, the 2-ethylhexanoyl chloride is added. The reaction is allowed tocontinue stirring with no heat overnight. The next day, GC confirms thereaction is complete.

All three batches are combined in a 2000 mL, three-neck, round-bottomflask. A thermometer and an overhead mechanical stirrer are added. 300mL of methanol is added to sample. The stirrer is started. The sample isallowed to mix for 30 minutes. The sample is put on the rotavap toremove the toluene and methanol. 431.04 g are recovered. The acid numberis tested and found to be 5.39 mg KOH/g. 50.65 g of sodium hydroxide(NaOH) pellets are added to the flask and a stirrer, and the samplestirred overnight. The next day, 500 mL of hexane is added, and thesample is poured down a column that is one-quarter filled with silica 60gel. Once the sample is pulled through, the column is rinsed with 2aliquots of 100 mL each hexane. After the rotavap, 357.78 g isrecovered. The sample is run down the WFE using the same conditions asearlier to remove any excess solvent. The overheads are discarded.

1. A dielectric fluid composition for electrical apparatus comprising a functionalized 12-hydroxy stearic acid having at least one property selected from: (a) a number average molecular weight from 400 Daltons to 10,000 Daltons; (b) a dielectric breakdown greater than 20 kilovolts/1 mm gap; (c) a dissipation factor less than 0.2 percent at 25° C.; (d) a fire point greater than 250° C.; (e) a kinematic viscosity less than 35 centistokes at 40° C.; (f) a pour point lower than −30° C.; (g) an acidity less than 0.03 mg KOH/g; and (h) a combination thereof.
 2. The dielectric fluid composition of claim 1, wherein the functionalized 12-hydroxy stearic acid is present in an amount ranging from 1 weight percent to 100 weight percent.
 3. The dielectric fluid composition of claim 1, wherein the functionalized 12-hydroxy stearic acid is present in an amount ranging from 30 weight percent to 90 weight percent.
 4. The dielectric fluid composition of claim 1, further comprising a natural triglyceride; a genetically modified natural oil; a synthetic ester; a mineral oil; a poly alpha olefin; or a combination thereof.
 5. The dielectric fluid composition of claim 1, wherein the number average molecular weight is from 400 Daltons to 5,000 Daltons.
 6. A process for preparing a dielectric fluid composition comprising (a) reacting 12-hydroxy methyl stearate and a linear or branched C3 to C20 alcohol under conditions suitable to form an alkyl-12-hydroxy stearate; and (b) reacting the alkyl-12-hydroxy stearate and a carboxylic acid selected from the group consisting of linear and branched C4-C20 free acid chlorides, fatty acids, carboxylic acid anhydrides, and combinations thereof, under conditions suitable to form a functionalized 12-hydroxy stearic acid.
 7. The process of claim 6, wherein the alcohol is selected from the group consisting of C8 to C10 alcohols.
 8. The process of claim 6, wherein the carboxylic acid is selected from linear and branched C8 to C10 fatty acids and carboxylic acid anhydrides.
 9. The process of claim 6, wherein the carboxylic acid is a linear or branched C8 to C10 free acid chloride. 